This invention is directed to threshold switching devices which exhibit negative differential resistance (NDR), and to certain ceramic threshold switching devices which are useful in the detection of reactive gases in a fluid stream.
Devices which exhibit threshold switching, and metal oxide devices which exhibit threshold switching with negative differential resistance (NDR), are known in the art. The switching and negative differential resistance (NDR) characteristics of silicon oxide films have also been described in the literature.
The use of thin film silica coatings derived from hydrogen silsesquioxane resin to provide protection and electrical insulation is not new, but the use of those coatings to form switching devices which are useful in the detection of reactive and inert gases is believed to be novel.
Coatings and switching devices formed by depositing a thin hydrogen silsesquioxane derived silicon dioxide film between at least two electrodes and applying a voltage above a threshold voltage across the electrodes, are described in detail in a prior copending patent application U.S. Ser. No. 07/694721 filed May 2, 1991 now U.S. Pat. No. 5,312,648, and entitled "Threshold Switching Devices".
Such coatings and switching devices have also been described in another copending application assigned to the same assignee as the present application, U.S. Ser. No. 07/915572, filed Jul. 20, 1992 now U.S. Pat. No. 5,283,545, entitled "Variable Resistors".
The present invention involves these coatings and switching devices and their utility in gas detection applications.
It has been discovered that switching devices with desirable features can be formed by depositing a thin hydrogen silsesquioxane derived silicon dioxide film between at least two electrodes, and applying a voltage above a threshold voltage across the electrodes. These ceramic devices are useful in the sensing of reactive gases present in a fluid stream.